1. Field of the Invention
The present invention relates to a parking brake system for use in vehicles, and, more particularly, to an electric parking brake system capable of achieving efficient operation while reducing generation of noise through the use of a motor and planetary gear unit.
2. Description of the Related Art
In general, a parking brake system is an apparatus to maintain a parked vehicle in a stationary state so as not to move, and serves to hold wheels of the vehicle so as not to rotate.
FIG. 1 is a perspective view schematically showing the partial configuration of a vehicle having a conventional hand-operated parking brake system.
As shown in FIG. 1, the conventional parking brake system comprises drum brakes 21 and 22 mounted, respectively, to a pair of wheels 11 and 12, a parking lever 30 to be operated by a driver, and a pair of parking cables 41 and 42 to connect the parking lever 30 to the brakes 21 and 22, respectively.
As known in the art, each of the brakes 21 or 22 includes a drum adapted to rotate along with the associated wheel 11 or 12, a pair of brake shoes movably mounted in the drum to be selectively compressed against an inner surface of the drum, an operating lever to operate each brake shoe, and a return spring to return each brake shoe to an original position thereof.
Each of the parking cables 41 or 42 has one end connected to the operating lever of the associated brake 21 or 22 and the other end coupled to an equalizer 50 that is connected to the parking lever 30. The equalizer 50 serves to allow the same load to be applied to the left and right parking cables 41 and 42.
In the conventional parking brake system having the above described configuration, if a driver pulls the parking lever 30 upward, both the parking cables 41 and 42 are pulled simultaneously, thereby causing each operating lever of the left and right brakes 21 and 22 to push the associated brake shoe to the inner surface of the drum. Thereby, as the brake shoes are compressed against the inner surface of the drum with the above described pushing operation, a braking force is applied to the drums and wheels 11 and 12, to prevent rotation of the wheels 11 and 12.
However, the conventional hand-operated parking brake system has an inconvenience in that the driver must pull the parking lever with an appropriately regulated force and suffers from a low space utility of a vehicle compartment due to a large operating radius of the parking lever.
To solve the above described several problems of the hand-operated parking brake system, an electric parking brake designed to automatically operate brakes using a motor has been proposed and actively developed to achieve an improved operating performance, reduced operating noise, and the like.